Investigate need for a workflow_dispatch on dep-image-1-start.yml workflow

[CodeGat]

Although it was added to be in compliance with the existing CI infrastructure, there might not actually be many cases in which one would want to create a base-spack/dependency image outside of the usual CI.

One potential need would be to kick off a build when we update containers/compilers.json or containers/models.json, but perhaps that would be better served by a CI check in build-ci itself, which calls the dep-image pipeline when those files are updated.

References a comment in #100 (specifically, #100 (comment))

[CodeGat]

Unassigning myself as Nirin runner stuff takes priority at the moment. Got a draft PR in.